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Customer Acquisition Cost Calculator: CAC, LTV:CAC, and Payback
Calculate fully loaded CAC and optional simple LTV, LTV:CAC, and CAC payback with visible units, assumptions, and invalid states.
- Method owner
- Anastasiia Krynytska
- Reviewed
- 10 Sep 2026
- Reading
- 8 min read
Practical answer
What this resource does
Enter an aligned cost pool and acquired-customer denominator; optional monthly inputs add simple unit-economics estimates without turning them into a health grade.
- No lead gate. Open, calculate, or download directly.
- Visible method. Definitions, formulas, ownership, and invalid states stay inspectable.
- Human authority. The asset supports a decision; it never owns one.
Browser-local tool · v1
Calculate CAC and optional unit economics
Your entries remain in this tab’s memory and clear on refresh.This calculator answers four bounded questions: how much fully loaded Sales and Marketing cost was incurred, how many new customers were acquired in the aligned period, what CAC follows from those inputs, and—when the additional inputs are valid—what simple LTV:CAC and CAC payback estimates result. It runs in the browser, requires no account or email, and does not send, store, cookie, or retain entered values.
The output is arithmetic, not a judgment label. The calculator shows the formula, substituted values, units, period, assumptions, validation messages, and optional comparison bands. It does not say that a business is “healthy,” “excellent,” or “failing.” Strategy depends on cash timing, retention shape, growth stage, channel, margin, expansion, customer concentration, and data quality.
Stripe’s CAC overview describes the common acquisition-cost relationship, and its CAC payback guide explains the recovery-period concept. Luck My Sales uses a strict fully loaded operating definition and makes alignment and invalid denominators visible.
01 / Method
The direct CAC formula
CAC = fully loaded Sales and Marketing expense ÷ new customers acquired in the same period.“Fully loaded” means costs needed to acquire the customer population in scope, not only advertising spend. Depending on the declared accounting policy, that can include Sales and Marketing payroll and employer costs, commissions or acquisition incentives, media, agencies, tools, data, events, content production, attributable contractors, and allocated overhead. The calculator does not dictate a financial-accounting policy; it requires the user to state and apply one consistently.
The denominator is new customers acquired in the same declared period and scope. Do not use leads, opportunities, users, subscriptions, or all active customers unless the metric is relabeled. If one customer signs several contracts, the customer-count policy must be explicit. If acquisition cost precedes customer creation by a long lag, the direct same-period estimate may be operationally useful but economically distorted; use a cohort or lag-adjusted analysis.
02 / Method
Input contract
The calculator offers two modes.
Direct mode accepts total fully loaded Sales and Marketing expense and new customers acquired. It is appropriate when the cost pool is already reconciled.
Cost-builder mode accepts visible components: compensation, media, tools and data, agencies and contractors, events and content, commissions or incentives, allocated overhead, and other documented acquisition cost. It sums the components before dividing. Empty optional components are treated as zero only after the interface says so; blank and unknown are not silently interchangeable.
Every calculation also records currency, period label, period length in months, customer population, and cost-policy note. Currency symbols do not convert values. Mixing dollars and euros, or monthly and annual inputs, produces a unit error even when the arithmetic runs.
Validation rules are deterministic:
- all monetary inputs must be finite and non-negative;
- new customers must be a positive whole number for CAC;
- period months must be finite and greater than zero;
- gross margin must be between 0% and 100%;
- churn inputs must use the declared percentage and period;
- direct and component cost modes cannot both control the same result;
- missing required inputs return Unavailable, never zero;
- division by zero returns a specific explanation, never infinity.
03 / Method
Optional simple LTV estimate
The owner-specified steady-state relationship is:
LTV = ARPU × gross margin ÷ net churn.The formula is available only when ARPU, gross margin, and net churn use the same recurring period and net churn is greater than zero. Here ARPU means average recurring revenue per customer in that period, and gross margin is entered as a decimal in the calculation. If monthly ARPU and monthly net churn are used, the result is in currency per customer.
This compact formula assumes a stable recurring population and a constant positive churn relationship. It is not suitable for every business. It can be highly sensitive when churn is small, it can hide cohort differences, and it does not model discount rates, finite contracts, retention curves, acquisition timing, or future margin changes.
When net churn equals zero or is negative because expansion offsets or exceeds contraction and loss, the steady-state division is not economically meaningful. The calculator returns Unavailable: use cohort contribution LTV. It must never display infinity or a negative lifetime value. A cohort contribution method sums realized and supportable forecast gross profit for a defined acquisition cohort across time, with explicit retention, expansion, service cost, and horizon assumptions.
04 / Method
LTV:CAC ratio
LTV:CAC = valid LTV estimate ÷ CAC.Both sides must refer to a compatible customer population, margin treatment, currency, and acquisition model. A blended CAC for all new customers should not be compared with an enterprise-only LTV. If CAC or LTV is unavailable, the ratio is unavailable.
The owner provides two contextual planning bands: LTV:CAC of at least 3:1 and approximately 4:1 for a mature SaaS context. The calculator presents these as Luck My Sales owner-supplied reference bands, not universal targets or empirical guarantees. A higher ratio is not automatically better: it can indicate underinvestment, constrained growth, stale cost allocation, optimistic LTV, or a genuinely strong economic model. The decision still needs capacity, cash, risk, and cohort evidence.
For a fuller explanation of acquisition-cost scope and common exclusions, read the customer acquisition cost guide. The calculator exists to produce reproducible arithmetic; the guide handles interpretation.
05 / Method
CAC payback
A simple gross-margin-adjusted monthly payback estimate is:
CAC payback months = CAC ÷ (monthly ARPU × gross margin).Monthly ARPU and monthly gross profit contribution must use compatible units. The calculation requires positive CAC, positive ARPU, and positive gross margin. When gross profit contribution is zero or unavailable, payback is unavailable rather than infinite.
This simple estimate assumes a stable monthly contribution and excludes timing complexities such as annual prepayment, delayed implementation, ramp, variable service cost, expansion, contraction, and bad debt. It is a planning approximation, not a cash-flow statement.
Owner-supplied comparison bands are payback at or below 12 months for a general SaaS context and at or below 8 months for an SMB context. They appear as sourced owner context with the period and scope, not as “pass” or “fail.” Stripe also discusses how CAC payback interpretation varies by company and model in its payback-period guidance.
06 / Method
What the result panel shows
The result panel presents:
- fully loaded cost total and included components;
- customer denominator and declared period;
- CAC with the substituted formula;
- simple LTV, if valid, with a method label;
- LTV:CAC, if both inputs are valid;
- payback months, if the monthly contribution is valid;
- assumptions and exclusions;
- contextual comparison bands, clearly separated from calculated results;
- warnings about alignment, low-denominator sensitivity, or invalid steady-state churn;
- a copyable, human-readable summary.
The interface will not store inputs in cookies or LocalStorage. Refreshing or closing the page clears state. A share action copies the inputs and formulas as text only when the user requests it; it does not create a public result URL in v1.
07 / Method
Worked example
This example is illustrative. A company declares $240,000 of fully loaded Sales and Marketing expense for a quarter and 40 new customers acquired under the same population and period rule.
CAC = $240,000 ÷ 40 = $6,000 per new customer.Suppose monthly ARPU is $1,000, gross margin is 80%, and monthly net churn is 2%.
Simple LTV = $1,000 × 0.80 ÷ 0.02 = $40,000 per customer.LTV:CAC = $40,000 ÷ $6,000 = 6.67:1.Payback = $6,000 ÷ ($1,000 × 0.80) = 7.5 months.These results do not prove that acquisition should be expanded. The analyst should inspect whether quarterly acquisition spend and customers are aligned, whether the monthly churn input reflects a comparable cohort, whether ARPU includes non-recurring revenue, whether 80% represents the relevant contribution margin, and whether implementation or service costs are omitted.
If the same example uses net churn of 0%, the calculator returns no simple LTV and no LTV:CAC. CAC and payback can still be shown because their valid inputs remain available. This partial-result behavior is safer than suppressing everything or manufacturing an infinite LTV.
08 / Method
Comparison and scenario use
Compare channels or segments only when cost allocation and customer definitions are consistent. Label blended, paid-only, sales-assisted, partner, organic, new-logo, and reactivation CAC separately. Shared costs may need a documented allocation driver. If a channel contributes across several periods, use cohort and lag analysis.
For scenario planning, change one visible driver at a time: total cost, customer count, ARPU, gross margin, or churn. The calculator shows the numerical change but does not imply causality. Lowering assumed churn is not an intervention; it is a scenario until supported by observed cohort behavior.
Recalculate at a cadence suited to the decision. Monthly values may be noisy for low-volume businesses. A rolling period can improve stability but may hide recent changes. Always show the period and customer count beside the metric.
09 / Method
Test vectors and expected behavior
The production implementation will be verified against deterministic cases:
- Expense 100, customers 10 → CAC 10.
- Expense 0, customers 10 → CAC 0, with a cost-scope warning.
- Expense 100, customers 0 → CAC unavailable; denominator error.
- Expense blank, customers 10 → CAC unavailable; required input missing.
- ARPU 100, margin 80%, churn 2% → simple LTV 4,000.
- ARPU 100, margin 80%, churn 0% → simple LTV unavailable; cohort guidance.
- ARPU 100, margin 80%, churn −1% → simple LTV unavailable; cohort guidance.
- CAC 1,000, monthly ARPU 200, margin 50% → payback 10 months.
- Margin 120% or negative expense → validation error; no output.
- Currency or period mismatch selected → explicit alignment warning.
Rounding occurs only for display. Internal calculations retain full numeric precision. The interface distinguishes percentage points from decimal inputs and makes the conversion visible.
10 / Method
Frequently asked questions
Should founder salary be included in CAC?
Include acquisition labor according to the declared fully loaded cost policy, even when cash compensation is atypical. For comparability, disclose the treatment and consider a normalized view.
Should customer success cost be included?
Not automatically in acquisition cost. Implementation or onboarding work required to acquire and activate a customer may need explicit treatment; ongoing service costs belong in margin or cohort contribution analysis. Apply one documented policy.
Can I use logo churn in the LTV formula?
Only if ARPU, margin, churn definition, and model assumptions are compatible. Revenue churn and logo churn answer different questions. Label the method precisely.
Why are there no colored health grades?
Because an arithmetic result cannot determine strategy without business context. The calculator provides objective output and labeled comparison bands, leaving the decision to accountable humans.
Is any input sent to Luck My Sales?
No. Version 1 calculates in the browser and uses no server storage, cookies, LocalStorage, or lead gate for calculator inputs.
Method owner: Anastasiia Krynytska, RevOps Architecture Lead. Reviewed 10 September 2026. Outputs are planning calculations, not accounting, investment, or financial advice.
Method & privacy note
Inspect before you act
- The complete approved editorial text is published on this page, not hidden behind the download or interface.
- Calculator inputs stay in browser memory; workbook contents stay wherever the user saves them.
- Unknown, unavailable, contradicted, and not applicable remain distinct states.
- Corrections: corrections@aiinsales.org.